BSTJ 14: 4. October 1935: Technical Digests: Marine Radio Telephone Service for Boston Harbor. (Gifford, F.A.; Meader, R.B.)

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Marine Radio Telephone Service for Boston Harbor *

By F. A. GIFFORD and R. B. MEADER

THERE has been a constantly increasing interest in an inexpensive
service for small harbor and coastal craft such as tugboats,
private yachts, coastal passenger ships, merchant craft and fishing
vessels. This interest became particularly evident in New England
in 1931 and since equipment suitable for the purpose had recently
been developed by Bell Telephone Laboratories, the New England
Telephone and Telegraph Company undertook the establishment of a
marine radio telephone service.

A survey consisting of a comprehensive series of field strength
measurements on shipboard and at various points along the coasts of
Massachusetts and Cape Cod Bays resulted in selecting Green Harbor
as the location for a shore station. Green Harbor is in the town of
Marshfield, Massachusetts, about 28 miles southeast of Boston.

A commercial survey indicated that initially the service would be
of interest chiefly to the Boston fishing industry. Consequently, boat
radio telephone equipment was installed on the trawler "Flow" of the
Bay State Fishing Company and the service was opened in June, 1932,
on a demonstration basis. As tests with this vessel progressed, it
became evident that the radio telephone service would fulfill the com-
munications requirements of the fishing industry. It also became
apparent that a complete service of this type should include some
means for determining the vessel's position at any time by means of
radio. Therefore, the development of such equipment was initiated
by Bell Telephone Laboratories as an adjunct to the radio telephone
service, and the outcome of tests of an experimental model indicates
that the problem of providing suitable radio compass equipment in the
price range satisfactory to the fishing fleet owners has been satis-
factorily solved.

The radio transmitter is a 400-watt crystal-controlled type similar
to those designed for use at aviation ground stations and adjusted to
operate at a frequency of 2506 kilocycles. This frequency is main-
tained within limits of better than 0.025 per cent.

In order to combine the two unidirectional radio channels into a two-
way circuit suitable for connection to the ordinary wire circuits in the

* Digest of a paper to be published in full in Communication and Broadcast
Engineering, October, 1935.

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land telephone network, apparatus similar to that provided at the
terminals of the transatlantic and high seas ship-to-shore radio tele-
phone circuits has been provided. This apparatus includes controls
for adjusting the volume of speech into the transmitter from the
receiver to the wire lines and the usual voice operated devices (termed
"vodas") provided for the suppression of echoes and singing.

The apparatus mentioned, together with a volume indicator, means
for talking, monitoring and signaling, and testing apparatus, is as-

Fig. 1 — Installation of control unit on fishing trawler.

sembled on one floor-mounted apparatus bay. This, mounted ad-
jacent to the bay containing the receiver and a noise suppression de-
vice, constitutes the operating position. This position is continuously
attended by a technical operator who adjusts the controls during the
progress of each call, guided by indications of the meters provided, to
insure the best possible connection under the conditions obtained at
the time. Power for the terminal apparatus is supplied by a motor
generator set operating from a 110-volt 60-cycle source.

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The noise suppression device, termed a "codan" (carrier operated
device anti-noise) is employed in connection with the receiver which
introduces a predetermined high loss into the audio-frequency portion
of the radio receiver during intervals when there is no incoming carrier,
and insures relatively quiet conditions on the receiving line. When a
carrier is received, the codan action removes this loss, allowing the
speech with which the carrier is modulated to pass from the receiver

Fig. 2 — Marine radio compass installed on a trawler.

MARINE RADIO TELEPHONE SERVICE 705

output to the receiving line. This device makes it possible to deliver
higher speech volumes to the telephones on shore since it prevents the
operation of the receiving vodas relays on radio noise during the idle
intervals. It also prevents the high radio noise which would other-
wise result due to the increase in gain inserted by the automatic volume
control whenever the carrier is interrupted.

It can be seen from this discussion that the use of the codan pre-
supposes suppression of the carrier of the distant transmitter except
when the user wishes to talk. This method of operation has been
adopted for this type of marine radio telephone service.

A 10-kw. 220-volt three-phase 60-cycle alternator driven by a
Buffalo gasoline engine has been provided to furnish the necessary
emergency power supply in case the normal commercial supply fails.

The frequency designated by the Federal Communications Com-
mission for use by ships communicating with the shore through the
Green Harbor radio telephone station is 2110 kilocycles. This carrier
frequency is maintained within limits of 0.025 per cent.

Two crystals are provided and the circuit arranged so that the
receiver may be quickly adjusted to operate on either of two frequencies
by means of a local mechanical or an electrically operated remote
control. The receiver is so designed as to make possible boat-to-boat
conversations on a separate frequency.

The signaling unit which is normally connected to the output of the
radio receiver consists of a selector operated under the control of an
arrangement of relays which in turn are controlled by incoming signal
pulses of 600 and 1500-cycle tones. The bell on each vessel is oper-
ated only in response to the particular code of pulses to which the
selector is adjusted. Arrangements are also included so that the
vessels of any one fleet may be called simultaneously.

A motor generator set operates continuously while the vessel is
standing by for the reception of signals and furnishes 12- and 200-volt
power for the operation of the radio receiver and signaling unit. A
second motor generator set is automatically started when the handset
is lifted from the switch hook to place a call or in response to an in-
coming signal, and furnishes power to operate the transmitter. On
several of the smaller boats having 32-volt power supply with wide
voltage fluctuations, power supply equipment consisting of two
dynamotors operated from a 12-volt battery charged from the vessel's
storage battery has been employed successfully.

The control unit for the radio telephone consists of a small panel on
which are mounted a switch for turning the set on and off, a meter for
indicating antenna current, a manual volume control, pilot lamp

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signals and a bell for announcing incoming calls. A special handset
with push button completes the control unit assembly.

At Boston, the marine radio telephone traffic is handled at two
positions on the outgoing toll board especially modified for this pur-
pose. The wire lines from the Green Harbor station terminate at this
point, and calls from vessels can be switched by the operator to any
point connected to Bell System facilities. The normal wire lines are
three loaded cable pairs. One pair is used for transmission from the
shore telephone to a boat, the second conducts speech received from a
boat through the toll position to the land line telephone, and the third
is employed as an order wire for communication between the operator
at the marine position and the technical operator at the Green Harbor
station. All of these circuits are duplicated over an alternate route
for use in case of trouble on the normal facilities.

The marine operator dials the code assigned to the vessel desired.
The dialing operation produces the desired grouping of 600 and 1500
cycle pulses which modulate the radio transmitter carrier frequency
of 2506 kilocycles. The signaling unit on the vessel is actuated by
these pulses and the bell rings. The captain raises the handset from
the switch hook on the control unit, presses the push button in the
handle of the handset and announces the name of his vessel. The
operator then completes the connection and the conversation takes

place.

In placing a call from boat to shore the captain or member of the
crew raises the handset from the switch hook and, after listening to
ascertain that no conversations are in progress, presses the push button
and calls "marine operator." The marine operator who is normally
monitoring on the channel ascertains the name of the calling vessel,
the shore station desired and other necessary details, and while the
calling party holds the line proceeds to call the land line telephone and
establish the connection.

When a person on one boat wishes to talk with a person on another
boat, the procedure in placing the call and establishing the connection
is the same as in the case of a ship-to-shore call, except that when both
are prepared to talk, the technical operator at Green Harbor operates
a by-pass key which connects the radio receiver output and radio
transmitter input without including the voice operated device and
other equipment associated with the land circuits. The land line is
bridged onto the circuit so that the marine operator may be advised of
any difficulties which arise in carrying on the conversation.

During the more than two years that the system has been in experi-
mental service, the transmission results up to distances of 500 miles

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from the shore station have been quite satisfactory. Of course, during
periods of abnormally heavy static the normal range is somewhat
reduced. The service is available at all times, but practically all
business is handled between the hours of 8 A.M. and 6 P.M. so that
the relatively poor atmospheric conditions usually existing during
summer nights do not adversely affect the radio telephone traffic.
However, experience has indicated that calls originated during such
periods from vessels within the normal range can be handled satis-
factorily. During some periods of favorable atmospheric conditions
experimental transmissions over distances greatly in excess of the
normal range have been successfully conducted.

On fishing vessels the radio telephone equipment is accessible for
maintenance work only at the conclusion of trips which are usually of
about ten days' duration. It is obvious, therefore, that the equipment
must be designed for reliable operation over long periods and experience
indicates that these requirements have been well satisfied.

Fishing craft normally make use of the service for reporting the
details of the catch, for making arrangements to return to port and for
talking with other fishing vessels to locate points where fishing is best.
The radio telephone has proved of vital importance on several occasions
where engine breakdowns necessitated advice from shore in order to
make repairs and having replacement parts available upon the vessel's
arrival at port. In several instances of sickness and accidents to
members of a crew, medical advice has been obtained or the Coast
Guard summoned to remove the injured man for quick transportation
to a hospital. In one case of severe damage to a trawler as a result of
a collision, the Coast Guard were summoned and the owners were able
to keep in constant touch with the situation.